[FEATURE]: Implement MCP Apps AppBridge same-server authorization path

[vishu-bh]

Parent epic: #2527

User Story

As an MCP App developer, I want AppBridge calls to tools/resources to be authorized through the same server and session context so that apps cannot cross boundaries or bypass RBAC.

One-Week Deliverable

Implement the server-side AppBridge authorization/routing path for app-originated JSON-RPC calls under generic extension governance.

Acceptance Criteria

• UI view sessions bind app calls to a specific server, UI resource, caller, token scope, team scope, and MCP session.
• AppBridge tools/call and resources/read enforce same-server constraints.
• RBAC, token scoping, extension enabled state, server visibility, and tool/resource visibility are checked before execution.
• App-originated calls run through plugin, sanitizer, audit, and observability hooks.
• Cross-server app calls are denied and audited.
• Expired, missing, forged, disabled-extension, wrong-team, and insufficient-permission UI sessions are denied.
• Tests cover allowed same-server calls, cross-server deny, expired session deny, disabled extension deny, wrong-team deny, and insufficient-permission deny.

Demo

From a simulated app session, call an allowed same-server tool successfully, then attempt a cross-server call and show it denied with an audit event.